Power lines are used for transporting the electric energy from generating power plants to electric substations and, in case of alternate current (AC) transported at high voltage (HV; typically higher than 30-35 kV) three-phase cables are typically used.
Ordinary and extraordinary maintenance need to be performed on power lines, especially in the substations, where voltage is transformed from high to low, or the reverse, overhead power lines are connected to cabled lines, and several other functions of the electric network are performed. Maintenance of the power lines can imply, for refurbishment and reconstruction of tower and overhead power lines; restoration or expansion in substations; inspection and/or replacement of power transformers, circuit breakers, switchgears, shunts, or other components of a substation. Such operations are performed by disconnecting all the components involved in the maintenance activity from the electric transmission line. Temporary by-pass systems linking input and output points within the substations are used in order to guarantee the continuity of electric power supply to the users during the maintenance period. Typically, the by-pass systems are constituted by several elements, as described, for example, in HVSBL January 2006 by Silec Cable (www.sileccable.com/Portals/france/pdf/en/2151_HVSBL.pdf).
According to this publication, a three phase High Voltage Stand-By Link (HVSBL) system is composed of three lengths of cable equipped with two synthetic terminations pre-mounted in factory; three dedicated drums allowing storage, transportation and unwinding and rewinding of the lengths equipped with their terminations; six metallic structures for supporting the terminations during use (optional).
The illustrated link systems are conditioned on dedicated metallic drums fitted out to contain and protect the cable equipped with its two terminations. A three phase link system may comprise from one single drum of 2.6 m in diameter equipped with three compartments allowing to install on the same drum the three phases of a 90 kV HVSBL of 20 m, to three specific drums of 4.7 m each one containing one phase of a 225 kV HVSBL of 350 m. Generally, the terminations are installed in protections (tube or under-frame) positioned and fastened on the inner side of the drum (for transportation). Termination length increases with voltage and can be comprised between 1.8 m for 90 kV and 2.8 m for 225 kV. The possibilities offered as regards lengths and reels are extensive but if important lengths (higher than 200 m) are chosen, it is necessary to plan special means for unloading, unwinding and transportation; as such, the period of implementation may be affected. Drums delivered, laying equipment and routine tools are transported by truck from a storage yard to the installation site.
The installation procedure of links for a three-phase network comprises the following steps:
unloading three drums, each carrying a phase link, from a truck by a crane;
unwinding the cable length of each link from the drum and lay it down to the site of connection of the outdoor termination thereof;
providing the site of connection with a supporting structure for each outdoor termination of each link;
connecting each outdoor termination to the overhead network line and the other cable end to another power line.
This procedure takes a substantial amount of time and staff, and this is a critical, especially in case of a line failure to be restored.
Due to the necessity of maintaining or repairing power lines, by-passing certain positions or points of an electric energy transmission line is usually a mandatory operation to guarantee safe condition and to guarantee the electric power supply to the users.
The Applicant has observed that it would be advantageous to have short operating time for providing by-pass on power lines.
In particular, the Applicant has tackled the problem of providing a by-pass module for power lines which requires shorter time and few staff for being installed in the field, compared with conventional ones.